This application is based upon and claims the benefit of priority from the prior Japanese Patent Application No. 2000-286790, filed Sep. 21, 2000, the entire contents of which are incorporated herein by reference.
1. Field of the Invention
The present invention relates to an optical disk drive unit by use of a medium such as CD (compact disk) or DVD (digital versatile disk). More particularly, the present invention relates to an optical disk drive unit that identifies target data read out from a medium, and that carries out control for transferring data to a buffer RAM; a decoder provided at the optical disk drive unit; and a buffer access circuit.
2. Description of the Related Art
Conventionally, for a CD-ROM or DVD-ROM drive unit, a DSP (digital signal processor) or the like is used as an input device provided in a CD player circuit or a DVD player circuit, the input device inputting data to a host CPU or the like. Then, in a process of acquiring data from this input device, and outputting the acquired data to an output device such as CPU after signal processing, it is required to temporarily store data in a buffer RAM in order to compensate for error correction or a difference in transfer speed between the input and output devices.
The data from the input device is stored in the buffer RAM in units of sectors. In this case, for the purpose of the convenience of signal processing such as error correction, data from a sector earlier than a sector required to be stored in the buffer RAM is outputted from the input device. The data stored in the buffer RAM is sequentially read out to be outputted to the output device. Therefore, the buffer RAM is used as a ring buffer. In this way, in order to use the buffer RAM as a ring buffer, it is required to recognize and manage a specific address instead of reading and writing data in batch.
In the meantime, in the input device, for example, in the CD-ROM drive unit, reproduced data from a CD player circuit is transferred to the buffer RAM in units of sectors to be stored in the buffer RAM. At this time, it is required to recognize and manage a specific sector address. In addition, at this time, data is recognized in units of sectors at a cycle of a synchronizing pattern.
When writing into the buffer RAM is started, positional information on a disk, header data, ID data, and sub-code Q data are extracted from CD-ROM, DVD and CD audio, respectively. It is required to detect a sector from these items of data, and know a reproduction position on an optical disk. A control microcomputer is used in order to recognize a position relevant to a target sector from the positional information on the optical disk.
In the meantime, data is sequentially inputted during access to the buffer RAM, thus making it necessary to set transfer start earlier than when the head of the target sector is inputted.
In this way, when data is transferred from the target sector data (target data) to the buffer RAM, and is written therein, header data earlier by one sector of the target sector or plurality of sectors is detected conventionally. When data obtained when the target sector is predicted to be inputted is detected earlier by one sector, data transfer to the buffer RAM is started from the next sector. When the data is detected earlier by a plurality of sectors, data transfer to the buffer RAM is started later by the plurality of sectors.
FIG. 1 is a timing chart showing an exemplary operation of a conventional optical disk drive unit configured to detect header data earlier than the target section by one sector, and transfer data to the buffer RAM.
A synchronizing detection signal is obtained by detecting header data of each sector. A control microcomputer reads out header data based on this synchronizing detection signal (header data reading). The control microcomputer judges whether or not the read out header data is a sector (n-1) earlier than a target sector (n) by one sector. When the judgment result is affirmative, the control microcomputer issues a transfer start command (i.e., issues a microcomputer transfer start command). A writing period signal is generated upon the receipt of this command, and writing from the data on the target sector (n) to be inputted into the buffer RAM is started based on this writing period signal.
In order to carry out the above described writing processing, the control microcomputer reads out header data, checks a sector position, and judges whether transfer start is enabled or disabled. Thus, a tremendously large amount of time is required for the above processing. In particular, in the recent CD-ROM drive unit or DVD drive unit is practically used such that a speed of reading out data from a disk is xe2x80x9cnxe2x80x9d times such as 2, 4, or 16 times as high as a standard speed. In this drive unit whose readout speed is xe2x80x9cnxe2x80x9d times as high as the standard speed, the period occupied by each sector is very short as compared with a case of the standard speed. Because of this, a control microcomputer requiring high speed processing and being expensive is used.
In addition, conventionally, transfer is started at a position at which a target sector is predicted to be reproduced, and there is no means for actually check the header data of the target sector before starting transferring. During disk reproduction, external shock is applied, or a track jump occurs due to a scratch on the disk or any other reason. Thus, there cannot be solved a problem that data cannot be correctly read out due to an incorrect data sector or disk eccentricity.
The above described problem occurs in the same way in the DVD-ROM drive unit as well.
As described above, conventionally, when data writing processing is carried out for the buffer RAM, a tremendously large amount of time is required for control microcomputer processing.
Further, conventionally, the header data on the target sector cannot be actually checked before starting transferring.
According to one aspect of the present invention, there is provided a buffer access circuit in an optical disk drive unit, comprises:
a buffer RAM for temporarily storing data;
a target register for storing positional data on an optical disk for target data recorded in the optical disk;
a comparator connected to the target register, for comparing positional data on the optical disk for the data read out from the optical disk with the positional data stored in the target register;
a delay circuit for delaying data read out and reproduced from the optical disk for a predetermined period; and
a buffer access control circuit connected to the comparator, the delay circuit and the buffer RAM, for carrying out control for starting transfer of data to the buffer RAM from the data that corresponds to the target data of the data outputted from the delay circuit, according to a control signal outputted from the comparator when the positional data stored in the target register coincides with the positional data on the optical disk for the data read out from the optical disk.